This invention relates to exchange and switching systems of the so-called common medium type, particularly adapted for use at optical frequencies.
With the advent of each new electrical or electronic technology, there has typically been an effort to determine its significance for switching in a communication system such as a telephone system. Thus, when tunable filters have been developed in the past there have been subsequent attempts to develop frequency-dependent switching systems that would simplify trunking in the communication system. For example, several prior patents have been directed to so-called common medium multichannel exchange and switching systems to achieve such objectives. One such patent is U.S. Pat. No. 2,064,896 to L. Espenschied et al., issued Dec. 22, 1936. Another is U.S. Pat. No. 2,345,048 to O. Myers et al., issued Mar. 28, 1944, which shows modifications of the Espenschied system directed to application within a central office. These prior systems apparently did not stimulate wide application.
One characteristic of such a system is that, when the number of channels is less than the number of customers or facilities to be switched, the switching logic is effectively transferred to another circuit which controls the frequency-dependent switches. The need for this degree of central control or information processing in the prior systems and the lack of any sufficiently compensating advantages over more conventional systems, made them less attractive than the conventional systems, e.g., crossbar switching systems, even though the latter required a greater number of switches in a typical communication path.
With the advent of the new technology of integrated optics, the attempt to construct optical switching systems on a direct analogy to existing widely used switching systems at lower frequencies fails to recognize much of the unique potential of communication at optical frequencies. Foremost with regard to this potential is the enormous bandwidth available at optical frequencies, so that channels of sufficient bandwidth to afford new and different services become attractive.
It is, therefore, an object of my invention to make more effective use of the unique characteristics of optical systems in implementing an optical switching system.